Electrosurgical procedures are advantageous since they generally reduce patient bleeding and trauma. The devices used are electrically energized, typically using an RF generator operating at a frequency that ranges between 100 kHz to over 4 MHz. Due to their ability to provide beneficial outcomes with reduced patient pain and recuperation time, electrosurgical devices have recently gained significant popularity recently. In common terminology and as used herein, the term “electrode” can refer to one or more components of an electrosurgical device (such as an “active electrode” or a “return electrode”) or to the entire device, as in an “ablator electrode” or “cutting electrode”. Electrosurgical devices may also be referred to as electrosurgical “probes” or “instruments”.
Many types of electrosurgical instruments are currently in use, and can be divided into two general categories: monopolar devices and bipolar devices. In the context of monopolar electrosurgical devices, the RF current generally flows from an exposed active electrode, through the patient's body, to a passive, return current electrode that is externally attached to a suitable location on the patient body. In this manner, the patient's body becomes part of the return current circuit. In the context of bipolar electrosurgical devices, both the active and the return current electrodes are exposed, and are typically positioned in close proximity to each other, more frequently mounted on the same instrument. The RF current flows from the active electrode to the return electrode through the nearby tissue and conductive fluids.
The need to effectively yet minimally invasively treat tumor tissue from a patient's body arises in the context of many medical practice areas, including, but not limited to, oncology, ear nose and throat (ENT), urology, gynecology, laparoscopy and general surgery. More specifically, there is often a need to denaturize, desiccate or coagulate tissue and destroy tumors in the liver, kidney, breast, lung, bone, lymph nodes, nerve ganglia and other organs. Such procedures are collectively referred to as tissue ablation or lesion formation, and are often used to destroy tumors without radical surgery. In such cases, an effective treatment is one in which the tumor itself, and perhaps a small margin of tissue around the tumor, is affected. The affected tumor tissue is not immediately removed. Over time, the dead tissue will naturally shrink, dissolve and, in some cases, be gradually replaced by scar tissue.
Although the benefits of these procedures are well recognized by those of skill in the art, current electrosurgical instruments and procedures suffer from very significant deficiencies. Quite often existing instruments are composed of one or more needles which are electrically energized by radiofrequency. As a result, the energy deposition in the tissue is concentrated close to where the needle is positioned, leading to overheating in the immediate region and under-heating in areas farther away. The result is a highly non-homogeneous energy deposition and highly non-homogeneous lesion. It is inherently impossible to accurately control the shape and size of the lesion formed with existing instruments because the energy deposition and heating occurs from the inside out. However, in order to destroy a tumor, it is often necessary, yet undesirable, to also destroy a large margin of healthy tissue around the tumor. As a result the current processes are inefficient, require high power levels and therefore can lead to unnecessary complications and undesired side effects. In some cases, additional return electrodes (also called grounding pads or patient electrodes) are needed in order to safely handle the high energy and high current required to perform the procedure. One such system marketed by Boston Scientific (Natick, Mass.) for lever ablation uses four patient electrodes simultaneously.
In view of these and other deficiencies, there is a need in the art for improved electrosurgical instruments that are capable of creating uniform lesions of a desired size and shape, capable of treating tissue and tumors from the outside in rather than from the inside out, and capable of treating large and non uniform tumors and leaving healthy tissue unharmed. There is also a need in the art for a high efficiency electrosurgical instrument capable of destroying the tumor at relatively low power, thereby increasing patient safety and efficacy and reducing undesired side effects.